Keyless access systems are known, for example from German specification DE 38 20 248 A1. This system comprises a portable radio transmitter, a manually actuated triggering switch mounted on the vehicle, a control device which is also connected to actuating devices and a further antenna, also mounted in or on the vehicle, which comprises a first frame antenna having a magnetic field formed substantially parallel to the center line of the vehicle and a second frame antenna having a magnetic field substantially transverse to the center line of the vehicle. The second frame antenna is said to be located between an outer and an inner surface of the vehicle near the triggering switch.
Recognition of the direction of incidence of the electromagnetic radiation emitted by the portable transmitter is neither provided for nor, with the antenna structure described, does it appear to be possible with the desired accuracy for the application contemplated here.